diff --git a/app/controllers/issues_controller.rb b/app/controllers/issues_controller.rb
index 7e65103..c8778b4 100644
--- a/app/controllers/issues_controller.rb
+++ b/app/controllers/issues_controller.rb
@@ -96,8 +96,10 @@ class IssuesController < ApplicationController
         format.pdf  { send_data(issues_to_pdf(@issues, @project, @query), :type => 'application/pdf', :filename => 'export.pdf') }
       end
     else
-      # Send html if the query is not valid
-      render(:template => 'issues/index.rhtml', :layout => !request.xhr?)
+      respond_to do |format|
+        format.any(:html, :atom, :csv, :pdf) { render(:template => 'issues/index.rhtml', :layout => !request.xhr?) }
+        format.api { render_validation_errors(@query) }
+      end
     end
   rescue ActiveRecord::RecordNotFound
     render_404
diff --git a/test/integration/api_test/issues_test.rb b/test/integration/api_test/issues_test.rb
index 763cf34..3dbd229 100644
--- a/test/integration/api_test/issues_test.rb
+++ b/test/integration/api_test/issues_test.rb
@@ -101,6 +101,16 @@ class ApiTest::IssuesTest < ActionController::IntegrationTest
           }
       end
     end
+    
+    context "with invalid query params" do
+      should "return errors" do
+        get '/issues.xml', {:f => ['start_date'], :op => {:start_date => '='}}
+        
+        assert_response :unprocessable_entity
+        assert_equal 'application/xml', @response.content_type
+        assert_tag 'errors', :child => {:tag => 'error', :content => "Start date can't be blank"}
+      end
+    end
   end
 
   context "/index.json" do